Antenna pattern simulator

ABSTRACT

A simulated antenna polar pattern signal is generated by apparatus including a 6 inch pattern wheel driven by a synchronous motor. The pattern wheel is a dielectric disc with copper plating on predetermined portions of one side of the disc and a stationary metal probe mounted flat against the other side of the disc. Rotation of the disc relative to the probe forms a varying capacitance in a circuit that modulates a carrier signal in accordance with the antenna polar pattern.

' United States Patent [191 Barron 1 Apr. 10, 1973 41 ANTENNA PATTERN SIMULATOR 3,517,282 6/1970 Miller ..317 249 3,146,398 S 1964 Schnad lb h... [75] Inventor: Morris Barron, Philadelphla, Pa. 3,154,739 51964 s i [73] Assignee: The Unit d Stat f A i as 1,823,360 9/1931 Heising represented by the Secmary of he 2,681,264 6/1954 Schnutt etal ..325/67 x N Primary ExaminerBenedict V. Safourek Flledi 1971 Attorney-R. S. Sciascia and Henry Hansen 21 A l. N 116 782 1 PP 1 57 ABSTRACT [52] U 8 Cl 325/67 317/250 325,363 A simulated antenna polar pattern signal is generated [51] by apparatus including a 6 inch pattern wheel driven [58] i 325/67 148 184 by a synchronous motor. The pattern wheel is a 325/3 334/58 dielectric disc with copper plating on predetermined Mil/242 249R 1, 7 3, portions of one side of the disc and a stationary metal probe mounted flat against the other side of the disc.

' Rotation of the disc relative to the probe forms a vary- [561 Refer Cm ing capacitance in a circuit that modulates a carrier UNITED STATES PATENTS signal in accordance with the antenna polar pattern.

3,255,414 6/1966 Kawalek et al. ..................325/184 X 6 China, 4 Drawing Figures I SYNC. MOTOR a SYNCHRO DISPLAY INPUT OUTPUT Z3 INSULATOR ANTENNA PATTERN SIMULATOR STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION The present invention generally relates to simulators and more particularly to simulators that produce an electrical signal which is an analog of a transmitted or received signal of any specified antenna with respect to readily available at laboratories and often involvea SUMMARY OF THE INVENTION Accordingly, it is a general purpose and object of the present invention to provide an improved antenna polar pattern simulator capable of a high degree of reliability. Another object is to provide a simulator of lower cost, higher reliability and less complexity and bulk than those heretofore known.

This is accomplished according to the present invention by a simulator board functioning as a variable capacitance in a tank circuit that modulates a carrier frequency by shifting the resonant frequency of the tank circuit. The modulating circuit generates the antenna pattern signal information. The modulated carrier signal is then applied to a detector circuit that provides for its output an electrical analog of the antenna signal for use in testing systems within the radar device. The system further generates a signal indicative of the angular position of the generated antenna pattern signal information.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic and block diagram partially in cross section of a simulator constructed according to the present invention;

FIG. 2 represents a view of the disc of FIG. 1 in the direction of the arrows 22;

FIG. 3 is a schematic diagram of the input-output circuit of FIG. 1; and

FIG. 4 is a graph of the voltage-frequency bandwidth of a tank circuit of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing and more particularly to FIG. 1 there is shown a synchronous motor 10 mechanically coupled by means of a drive shaft 11 to both a dielectric disc 12 and a synchro 13. The synchro 13 is rotated by shaft 11 and provides an electrical output to plan position indicating display 41. The dielectric disc has a copper conductor 14 on one side which is electrically grounded through slip ring or brush 17. A conductivescanning probe 18 makes radially sliding contact with the other side 15 of the disc 12. The conductive probe 18 is narrow so that it makes contact with only a small arc of the disc. A conductive spring contact 19 is fixed to insulator block 20 and electrically connects probe 18 to an input-output circuit 29. Inputoutput circuit 29 has contacts 28, 44, 45 and 46.

A fixed capacitor 21 in circuit 29 (FIG. 3) is electrically connected at terminal 44 to the disc 12, shown in FIG. 3 as a variable capacitor, through the spring contact 19. The other terminal of capacitor 21 is connected to the secondary side of transformer 22. The primary winding of transformer 22 has its input at terminals 45 and 46 and provides a 22.5 mHz carrier frequency input to the system. Both the primary and secondary windings of transformer 22 have one side grounded. The series connection of capacitor 21 and variable capacitor 12 in parallel with the secondary winding of transformer 22 provides a tank circuit 40 for the system. The secondary winding of transformer 22 functions as an inductor in the tank circuit 40. The common junction of capacitor 21 and the secondary winding of transformer 22 is connected to the cathode of diode 25. The anode of diode 25 is connected to a parallel circuit comprising a resistor 26 and fixed capacitor 27. Both resistor 26 and capacitor 27 have their other contacts grounded. A signal output indicative of the antenna pattern is provided from the contact 28 located at the junction of diode 25, resistor 26 and capacitor 27.

FIG. 2 provides a more detailed representation of disc 12 comprising a 6 inch diameter 1/32 inch thickness insulated dielectric circuit board partially plated on one side with copper with the board part acting as a dielectric. The discs are made from commercially available single copper plated circuit board material. The pattern is reproduced on the copper plating side with that portion of the copper not representative of the antenna field being etched away by means of a standard printed circuit board etching process. The copper 30 remaining on the wheel represents a polar plot of the desired antenna pattern. A copper circular section 31 is provided in the center of the disc for con-' necting the variable capacitor formed by the disc 12 to the remaining components in the system. The amount of copper 30 remaining 'on the disc in a radial direction is a function of the strength of the signal at that point.

In order to determine the configuration of the copper conductor 14 on the disc 12, either manufacturers test reports or point by point plots of antenna gain obtained in the field can be reproduced on the disc 12. The pattern etched on the disc 12 is then an actual point by point plot of the antenna gain with the amount of copper on any radius a direct function of gain at that angle. It is to be noted that at boresight the copper in the antenna pattern 30 makes contact with the grounded copper circular section 31 to complete the circuit. In addition side lobes 33 and 34 can be seen on the disc. A hole 35 is located in the center of the disc 12 through which the shaft 11 is mounted. The rotation of the disc 12 is shown by an arrow on the disc 12 surface.

The operation of the device will now be described with reference to the figures. A carrier signal of 22.5 ml-Iz is applied to transformer 22 and this carrier signal is amplitude modulated by the varying of the capacitance of disc 12 as it is driven by synchronous motor 10. A synchronous motor driven at rpm. was used to simulate a known antenna rotational rate, although any known rotational speed can be used as required.

In order to explain the output of the tank circuit 40 a look at FIG. 4 is useful. Curve e shows the output of tank circuit 40 when capacitor disc 12 is of a value to have tank circuit 40 resonant at 22.5 mHz. ln actual operation, however, the resonant frequency of tank circuit 40 varies between 22.45 ml-Iz as shown on curve f and 22.35 mHz as shown on curve g. Since the input frequency to the parallel tank circuit 40 remains at a constant 22.5 mI-lz, the amplitude of the modulated signal varies between the values at points F and G as the disc 12 rotates and its capacitive value varies. Diode 25, resistor 26 and capacitor 27 then act as a detector to the modulated signal and provide an output signal of the amplitude envelope of the vmodulated signal for testing purposes at contact 28.

The synchro 40, by direct connection to'the drive shaft 11, provides an electrical signal used to rotate an external indicator such as a cursor on a radar PPI display 41 in synehronism with the antenna disc 12. This provides an external visual reading on display 41 or a recorded presentation (not shown) representative of the angular displacement of the antenna pattern simulator.

There has therefore been shown a device for providing an antenna signal in which a disc 12 providing variable capacitance in a tank circuit 40 modulates a carrier signal. This modulated signal is supplied to a detector that provides antenna signal information. Such a wheel can be made for each antenna so that testing of individual radar systems may be conducted in a laboratory instead of an on-site location.

An alternative arrangement on disc 12 would be to have a pattern etched with the amount of copper extending outwardly from the center of the disc 12 instead of inwardly from the outer periphery as shown.

It will be understood that various changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

What is claimed is:

l. A signal generator comprising:

a cyclical variable resonant frequency tank circuit adapted to receive a constant input carrier frequency signal and providing an amplitude modulated output signal, said tank circuit including an inductor, and variable capacitance means connected in parallel with said inductor, said capacitance means having a dielectric disc with a central axis, an electrical conductor slidably contacting one side and along the radius of said disc,

5 rotatable about said axis relative to said disc, and

electrically connected to one terminal of said inductor, and a continuous annular conductor affixed about said axis to the other side of said disc and electrically connected to the other terminal of said inductor, the radial length of said annular conductor preselectively varying with disc rotation; and

detector means connected to said tank circuit for receiving said amplitude modulated output signal and detecting the amplitude envelope of said amplitude modulated output signal.

2. A signal generator according to claim 1 wherein said detector means further comprises:

a diode connected to receive and rectify the amplitude modulated signal;

a resistance-capacitance parallel circuit connected in shunt relationship to said diode; and

an output terminal for providing the envelope of the amplitude modulated signal.

3. An antenna pattern simulator comprising:

a synchronous motor;

a cyclical variable resonant frequency tank circuit adapted to receive an input carrier frequency and including a variable capacitance disc comprising a circuit board with one side copper plated in a first configuration forming a pattern representative of an antenna field and a second configuration surrounding the center of said circuit board forming a solid circular pattern and touching said first configuration, said variable capacitance disc rotatably connected to said synchronous motor for providing an amplitude modulated output signal having an amplitude envelope varying in amplitude of said pattern representative of the antenna field;

detector means connected to said tank circuit for receiving said amplitude modulated signal and detecting said amplitude envelope of said amplitude modulated output signal and having an output means for providing said amplitude modulated output signal;

a synchro rotatably connected to said synchronous motor for providing an output signal indicative of the angular displacement of said variable capacitance disc; and

visual display means connected to receive the output signal of said synchro for providing a visual indication of the angular displacement of said variable capacitance disc.

4. An antenna pattern simulator according to claim 3 wherein said tank circuit further comprises:

a fixed capacitance serially connected to said variable capacitance disc; and

a transformer winding connected in parallel to said serially connected fixed capacitance and variable capacitance disc.

5. An antenna pattern simulator according to claim 4 wherein said detector means further comprises:

a diode connected to receive and rectify the amplitude modulated signal;

a resistance-capacitance parallel circuit connected in shunt relationship to said diode; and

an output terminal for providing the envelope of the amplitude modulated output signal.

6. An antenna pattern simulator according to claim 5 wherein said visual display means further comprises a plan position indicator. 5

* i i i t 

1. A signal generator comprising: a cyclical variable resonant frequency tank circuit adapted to receive a constant input carrier frequency signal and providing an amplitude modulated output signal, said tank circuit including an inductor, and variable capacitance means connected in parallel with said inductor, said capacitance means having a dielectric disc with a central axis, an electrical conductor slidably contacting one side and along the radius of said disc, rotatable about said axis relative to said disc, and electrically connected to one terminal of said inductor, and a continuous annular conductor affixed about said axis to the other side of said disc and electrically connected to the other terminal of said inductor, the radial length of said annular conductor preselectively varying with disc rotation; and detector means connected to said tank circuit for receiving said amplitude modulated output signal and detecting the amplitude envelope of said amplitude modulated output signal.
 2. A signal generator according to claim 1 wherein said detector means further comprises: a diode connected to receive and rectify the amplitude modulated signal; a resistance-capacitance parallel circuit connected in shunt relationship to said diode; and an output terminal for providing the envelope of the amplitude modulated signal.
 3. An antenna pattern simulator comprising: a synchronous motor; a cyclical variable resonant frequency tank circuit adapted to receive an input carrier frequency and including a variable capacitance disc comprising a circuit board with one side copper plated in a first configuration forming a pattern representative of an antenna field and a second configuration surrounding the center of said circuit board forming a solid circular pattern and touching said first configuration, said variable capacitance disc rotatably connected to said synchronous motor for providing an amplitude modulated output signal having an amplitude envelope varying in amplitude of said pattern representative of the antenna field; detector means connected to said tank circuit for receiving said amplitude modulated signal and detecting said amplitude envelope of said amplitude modulated output signal and having an output means for providing said amplitude modulated output signal; a synchro rotatably connected to said synchronous motor for providing an output signal indicative of the angular displacement of said variable capacitance disc; and visual display means connected to receive the output signal of said synchro for providing a visual indication of the angular displacement of said variable capacitance disc.
 4. An antenna pattern simulator according to claim 3 wherein said tank circuit further comprises: a fixed capacitance serially connected to said variable capacitance disc; and a transformer winding connected in parallel to said serially connected fixed capacitance and variable capacitance disc.
 5. An antenna pattern simulator according to claim 4 wherein said detector means further comprises: a diode connected to receive and rectify the amplitude modulated signal; a resistance-capacitance parallel circuit connected in shunt relationship to said diode; and an output terminal for providing the envelope of the amplitude modulated output signal.
 6. An antenna pattern simulator according to claim 5 wherein said visual display means further comprises a plan position indicator. 